Solar Systems

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rhr22

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I am new to the Solar Industry. I am trying to figure out if a solar system (PV) is considered a separately derived system and should the system's neutral and ground be bonded at the it's disconnect with a GEC and ground rod? If the PV system is supply side tapped in service panel, wouldn't it create a parallel connection?
 
Short answer, no, a solar system is not an SDS. If there is an AC neutral from the solar that ties directly to the premises neutral then that is definitely not to be bonded again. Objectionable current and all that.

Longer answer...

Some older grid-tied systems have a transformer that isolates the solar side from the AC side. In that case you could argue that the DC side of the solar system is an SDS. But, when it comes to grounding solar systems, you follow article 690, not the stuff for SDS's in article 250. The same would be true for an off-grid system, even if there's also utility power on the site.

Most newer systems don't galvanically isolate the DC conductors from the AC conductors when operating, so are really not an SDS in any sense.

One clarification is that you can interconnect a grid-tied solar system through an SDS.
That is:
Utility <-> Transformer <-> Inverter
In this case you do treat the inverter side of the transformer as an SDS and follow the normal rules in article 250 for grounding a neutral at the transformer on the inverter side. When it comes to any grounding requirements for the inverter and solar, follow 690 again.
 
You also asked about a supply side tap. That brings up rules about bringing neutrals and GECs and bonding at service disconnects (although it has nothing really to do with SDS).

There's been a lot of debate on this forum as to whether a supply side tap is technically a service disconnect or not. What I would say is, either:
a) treat it like a service disconnect, and bond the neutral at the disconnect and bring a GEC tap to it
or
b) don't do any of that, and run an equipment ground and don't bond the neutral

Your inspector may or may not have a strong opinion that one or the other is the correct way to do it. I tend to lean towards (a), but I wouldn't try to argue the point with an inspector.
 
jaggedben said:
You also asked about a supply side tap. That brings up rules about bringing neutrals and GECs and bonding at service disconnects (although it has nothing really to do with SDS).

There's been a lot of debate on this forum as to whether a supply side tap is technically a service disconnect or not. What I would say is, either:
a) treat it like a service disconnect, and bond the neutral at the disconnect and bring a GEC tap to it
or
b) don't do any of that, and run an equipment ground and don't bond the neutral

Your inspector may or may not have a strong opinion that one or the other is the correct way to do it. I tend to lean towards (a), but I wouldn't try to argue the point with an inspector.
Click to expand...

I will only add my recommendation that you have a preconstruction meeting with the AHJ in any jurisdiction in which you want to install a supply side connected PV system and get on the same page with them as to whether it's a) or b). One major AHJ I deal with regularly differs on that point with every other AHJ in Texas.

BTW, if your PV system requires a transformer between the inverter(s) and the service, for example, when you interconnect 480V inverters to 208V services, the side of the transformer toward the inverter(s) IS separately derived as long as the transformer is not an autotransformer.
 
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